Foldable bicycles have been known for many years, e.g., the bicycle described in GB 2,287,438, in which the frame has a middle articulation joint which allows it to be folded by 180° about a vertical axis, after releasing a locking mechanism, in order to halve the longitudinal size of the bicycle and allow the latter to be eaily carried on a vehicle.
Other foldable bicycle are known, e.g., from DE 10 2007 013158 A1, wherein the frame consists of various frame parts hinged to one another about transverse axes and are interconnected for simultaneously rotating from an operative configuration to a folded, carrying configuration.
The above-described foldable bicycles have the drawback that the frame and the wheels are relatively small-sized, because they are designed to obtain a very compact folded configuration, to the detriment of the driving comfort and performance, which, in fact, are very limited, especially on uneven roads.
Moreover, even in their folded configuration, the above bicycles are heavy-weighted and sizable, so that they are not suitable to be carried by hand.
In the attempt of improving the driving comfort, WO/2006/131742 describes a foldable bicycle provided with standard-sized wheels. The frame has a front end and a rear end which are foldable about respective vertical axes, to which ends the two wheels are hinged. In particular, both the wheels of the bycicle of the above document are spokeless and are supported by a set of bearings engaged between the wheel and a respective guide attached to the frame. The lack of spokes allows some mechanical parts, such as the pedals, to be stored in the inner area of the wheels when the bicycle is folded, in order to reduce its overall size.
The above-mentioned bicycle, of course, is handier to be driven than the bicycles with small-sized wheels such as the one described in the above-cited document, GB 2,287,438, and the folding system makes it easier to carry the bicycle on a vehicle. However, the bicycle, even when folded, is yet too cumbersome to be carried by hand.
Furthermore, the above folding system having a frame provided with two articulation joints may be difficult to handle for the cyclist, who must handle the various parts of the frame while the latter is laying in precarious balance on the two wheels.
Nevertheless, although the use spokeless wheels is convenient because it reduces the weight of the bicycle, improves the aerodynamic properties, and prevents the risk of undesired locks caused by the intrusion of rigid bodies and/or limbs of the human body between the spokes, however the wheel-supporting system of the above document is liable to jamming in case of dust, sand or stones slipping into the bearings.
Other systems are known for connecting spokeless wheels to the frame of a bicycle, such as those described in U.S. Pat. Nos. 5,419,619 and 5,248,019, which provide for the use of an inner, stationary rim integral with the frame and an outer, rotary rim, with a crown of balls engaged between the rims. In other systems, such as the one described in U.S. Pat. No. 917,967, the wheel is locked by three rollers spaced from one another by two adjustable members.
With the above-cited systems, the advantages resulting from using spokeless wheels are limited, because the structure that connects the wheel to the frame is heavy and obstructs a considerable fraction of the inner area of the wheel.